Power Transformer Characteristics and Their Effect on Protective Relays

There are a variety of protective relays using different measuring techniques to provide reliable and secure transformer protection. This includes electro-mechanical, solid state and numerical relays. Within each group, various algorithms exist. Advancements made to transformer technology and design over the past 3 decades, have changed the characteristics of the transformer inrush current, and have often introduced incorrect operations in the existing harmonic restraint relays during energization. The paper discusses:

Comparison between old and newly developed more accurate calculations of peak values, magnitude of the second harmonic, and other parameters of Inrush current